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  • 1
    Electronic Resource
    Electronic Resource
    On the ultraviolet photofragmentation of hydrogen iodide (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 6174-6185 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An ab initio configuration interaction (CI) study including spin-orbit coupling is carried out for the ground and low-lying excited states of the HI molecule by employing a relativistic effective core potential for the iodine atom. The computed spectroscopic constants for the X 1Σ+ ground and b 3ΠΩ Rydberg states are in good agreement with available experimental data, as are the vertical excitation energies for the repulsive a 3Π1, a 3Π0+, and A 1Π1 states of the A band. The a 3Π0+ state is found to possess a shallow minimum of 600 cm−1 depth outside the Franck–Condon region, at (approximate)5.1 a0. The electric-dipole moments have also been calculated for transitions from the ground to the A band states. Contrary to what is usually assumed, the a 3Π1, A 1Π1←X0+ transition moments are found to depend strongly on internuclear distance. Employing the computed potential energy and transition moment data, partial and total absorption spectra for the A band are calculated and the I* quantum yields, ΦI*(ν), are determined as a function of excitation energy. The maximal ΦI*(ν) values are calculated to be 0.55–0.59 and lie at 39 000–40 000 cm−1, which agrees well with experimental results. The influence of the t 3Σ1+ state and of the nonadiabatic effects on the ΦI*(ν) values is found to be negligible in the essential part of the A band. Finally, it is shown that significantly higher I* quantum yield values (up to 0.8–0.9) may be achieved when vibrationally hot HI molecules are excited in the appropriate spectral range. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1308552
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  • 2
    Electronic Resource
    Electronic Resource
    Relativistic configuration interaction study of the ClF molecule and its emission spectra from 0+ ion-pair states (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 2274-2284 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An ab initio configuration interaction (CI) study including spin–orbit coupling is carried out for numerous valence and ion-pair states of the ClF molecule by employing relativistic effective core potentials. The computed spectroscopic constants are in good agreement with available experimental data for both valence and ion-pair states. The present calculations accurately reproduce the measured spin–orbit splittings for the first 3Π multiplet and confirm the recent corrected spectroscopic parameters for the A 3Π1 state [V. A. Alekseev, D. W. Setser, and J. Tellinghuisen, J. Mol. Spectrosc. 195, 162 (1999)]. The electronic structure of the six lowest ion-pair states of ClF which correlate to the Cl+(3P)+F−(1S) limit is analyzed in detail. It is shown that strong homogeneous perturbations of the E0+ and f0+, β1, and G1 states are mainly caused by an avoided crossing of the 3 3Π and 2 3 Σ− parent Λ–S states. The electric-dipole transition moments have also been calculated for transitions from the E and f ion-pair states to the lower-lying 0+ valence states. Emission spectra for the bound–bound and bound–free transitions have been computed on this basis and found to be in good agreement with the measured spectra. A similar analysis for the ion-pair D′2, β1, and G1 states will be presented in the subsequent study. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.480792
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  • 3
    Electronic Resource
    Electronic Resource
    Electronic states and transitions of bismuth sulfide (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 11294-11302 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The electronic spectrum of the BiS molecule is described by means of relativistic configuration interaction (CI) calculations employing effective core potentials. Spin-orbit coupling causes the Ω=3/2 components of the X 2Π and A 4Π Λ–S states to undergo an avoided crossing which causes perturbations to occur in the observed X2–X1 band system beginning at v′=5. The present calculations are able to explain these results on a nearly quantitative basis. Spectroscopic constants are computed for nine BiS states up to 20 000 cm−1 and generally good agreement is found between theoretical and available measured values. Four of these states have not yet been observed experimentally and thus the present results should aid in subsequent searches for them. In addition, radiative lifetimes and electric dipole moments have been calculated for each of the BiS states with the relativistic CI wave functions. Finally, these results have been compared in detail with the analogous spectral data for the isovalent BiO molecule. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479070
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  • 4
    Electronic Resource
    Electronic Resource
    Comparison of spin-orbit configuration interaction methods employing relativistic effective core potentials for the calculation of zero-field splittings of heavy atoms with a 2Po ground state (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 3400-3408 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Computational strategies for the treatment of relativistic effects including spin-orbit coupling at a highly correlated level are compared for a number of heavy atoms: indium, iodine, thallium, and astatine. Initial tests with perturbation theory emphasize the importance of high-energy singly excited configurations which possess large spin-orbit matrix elements with the ground state. A contracted basis consisting of L–S CI eigenfunctions (LSC–SO–CI) is found to give an accurate representation of both spin-perturbed 2Po components as long as key np→pi* singly excited configurations are included. Comparison is made with a more extensive treatment in which all selected configurations of various L–S symmetries form the basis for the multireference–spin-orbit–configuration interaction (MR–SO–CI). Good agreement is obtained with experimental SO splittings for the In, I, and At atoms at a variety of levels of treatment, indicating that the L–S contracted SO–CI approach can be implemented quite effectively with relativistic effective core potentials (RECPs) for both very electronegative atoms and also for lighter electropositive elements up through the fifth row of the periodic table. The thallium atom SO splitting is more difficult to obtain accurately because of greater differences between its valence p1/2 and p3/2 spinors than in the other cases studied, but good results are also possible with the contracted SO–CI approach in this instance, provided proper care is given to the inclusion of key singly excited L–S states. The relationship between all-electron two-component SO–CI treatments and those employing RECPs is also analyzed, and it is concluded that triply excited configurations relative to the 2Po ground state are far less important than previously reported. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475739
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  • 5
    Electronic Resource
    Electronic Resource
    The spectrum of arsenic hydride: An ab initio configuration interaction study employing a relativistic effective core potential (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 2028-2040 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An ab initio configuration interaction (CI) study including the spin–orbit interaction is carried out for numerous valence and Rydberg states of the AsH radical by employing a relativistic effective core potential for the arsenic atom. The computed spectroscopic constants are in good agreement with corresponding experimental data, with a tendency toward a slight overestimation of bond lengths (by 0.01–0.02 Å) and Te values (by 450–550 cm−1) for the lowest singlet states. Measured spin–orbit splittings for the X 3Σ− and A 3Π multiplets are also accurately reproduced in the present calculations and the Ω=0−, 1, and 2 components of the latter state are shown to be strongly predissociated due to spin–orbit interaction with the corresponding components of the repulsive 5Σ− state. Dipole moments μ(v=0) for the lowest-lying X 3Σ−, a 1Δ, and b 1Σ+ states, all arising from the (centered ellipsis)σ2π2 electronic configuration, are computed to have small (e.g., 0.1266 D for X1 3Σ0+−) and nearly equal positive values (As−H+ polarity). This finding is used to explain why the partial radiative lifetime for the parallel b–X1 transition (τp=44 ms) is much longer than that (τp=0.95 ms) of the perpendicular b–X2. The lifetime of the a 1Δ state is calculated to be 97 ms, significantly longer than that of the b 1Σ+ state, while the A 3Π substates have much shorter lifetimes (≤1 μs) for radiative decay to the X 3Σ− ground state. A number of other bound states and avoided crossings are indicated in the calculations which may be of relevance in future experimental studies of this system. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475582
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  • 6
    Electronic Resource
    Electronic Resource
    The spectrum of antimony hydride: An ab initio configuration interaction study employing a relativistic effective core potential (1998)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 108 (1998), S. 7695-7706 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An ab initio configuration interaction (CI) study including the spin–orbit interaction is carried out for numerous valence and Rydberg states of the SbH radical by employing a relativistic effective core potential for the antimony atom. The computed spectroscopic constants are in good agreement with available experimental data, with a tendency toward a slight overestimation of bond lengths (by 0.01–0.03 Å) and Te values (by 370–550 cm−1) for the lowest singlet states. Measured excitation energies and spin–orbit splittings for the A 3Π multiplet are also accurately reproduced in the present calculations and the Ω=0−, 1, and 2 components of this state are shown to be strongly predissociated due to spin–orbit interaction with the corresponding components of the repulsive 5Σ− state. The most stable representative of the A 3Π multiplet, A40+, is found to possess a very unusual potential curve with a double minimum and a fairly low barrier to dissociation. Based on a vibrational analysis of this state it is concluded that the earlier observed B0+ and C0+ electronic states should be attributed to the v=0 and 2 vibrational levels of the A40+ state, while the state experimentally assigned as A 3Π0+ corresponds to the A40+, v=1 level. Dipole moments μ(v=0) for the ...σ2π2 X3Σ−, a 1Δ and b 1Σ+ states are computed to have small (e.g., −0.238 D for X1 3Σ0+−) and nearly equal negative values (Sb+H− polarity). The dipole transition moments and the corresponding radiative lifetimes for a number of low-energy electronic transitions have also been computed. Many other bound states and avoided crossings are indicated in the calculations which may be of relevance in future experimental studies of this system. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.476205
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  • 7
    Electronic Resource
    Electronic Resource
    Theoretical study of the electronic spectrum of antimony oxide employing relativistic effective core potentials (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2539-2550 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Potential energy curves and electric dipole transition moments between different electronic states are computed for the antimony oxide molecule employing a relativistic configuration interaction scheme including the spin–orbit coupling interaction. Comparison is made with available experimental data as well as with the corresponding results which were recently reported for the isovalent BiO. A full core relativistic effective core potential proves to be quite effective in describing the antimony inner shells, thereby reducing the amount of computations considerably relative to an all-electron CI treatment. The calculated bond lengths re for the X1 2Π1/2 ground state and C 2Σ−1/2 excited state agree to within 0.01 A(ring) of the respective measured values and good agreement is also found for the vibrational frequencies ωe of a large number of SbO states. The theoretical treatment tends to underestimate transition energy Te values, typically by 1000–2000 cm−1, reflecting the fact that all excited states have more open shells in their leading configurations than does the ground state itself. On the basis of the present calculations it has been possible to confirm a number of earlier assignments for the SbO upper states and also to aid in the experimental detection of several new transitions involving various a 4Π and b 4Σ− species which were not known at the time this work was begun. Theoretical values for the radiative lifetimes of the v'=0 levels of each of the above electronic states have also been obtained, and they are found to agree within at least a factor of 2 in most cases with the recent experimental values obtained by Fink, Shestakov, and co-workers. The lone exception found to date is for the B 2Σ+ state, but it is noted that nonadiabatic interactions between it and the b1 4Σ−1/2 state, as already discussed in an earlier review by Rai and Rai, could be at least partially responsible for this result. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468683
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  • 8
    Electronic Resource
    Electronic Resource
    Spin–orbit configuration interaction study of the potential energy curves and radiative lifetimes of the low-lying states of bismuth hydride (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 100 (1994), S. 2989-3001 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: An ab initio configuration interaction (CI) study including the spin–orbit coupling interaction is carried out for the lowest 23 states of the bismuth hydride molecule by employing relativistic effective core potentials for the bismuth atom. The computed spectroscopic constants are in good agreement with corresponding experimental data, although there is a tendency to overestimate bond lengths by 0.05–0.10 A(ring) and to underestimate the vibrational frequencies accordingly. The B0+ excited state is found to have no dissociation barrier, and its radiative lifetime is computed to be 4.3 μs, with parallel transitions to X10+ being significantly stronger than the perpendicular B–X21 species. The experimental E0+ state is assigned as the third root of this symmetry and its potential curve possesses a dissociation barrier of 1840 cm−1. This result explains the predissociation characteristics observed for this state and is also consistent with the failure to observe emission from it when attempts are made to form it in recombination processes. This barrier also needs to be taken into account in estimating the X10+ dissociation energy of this molecule from existing experimental data, and on this basis a De value of 2.28 eV is obtained which is in reasonably good agreement with the present directly computed result of 1.98±0.06 eV. A number of other bound states and avoided crossings are indicated in the calculations which may be of relevance in future experimental investigations of this system.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.466440
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  • 9
    Electronic Resource
    Electronic Resource
    Spin–orbit configuration interaction study of potential energy curves and transition probabilities of the mercury hydride molecule and tests of relativistic effective core potentials for Hg, Hg+, and Hg2+ (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 4672-4684 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio CI calculations have been carried out for the low-energy states of the mercury hydride molecule HgH and its isotopomers. A relativistic effective core potential (RECP) given by Ross et al. [J. Chem. Phys. 93, 6654 (1990)] is employed to describe all but the Hg 5d and 6s valence electrons. Tests for a series of low-lying states of Hg, Hg+, and Hg2+ demonstrate that 0.1 eV accuracy is obtained at the SCF level with a high-quality basis set for this RECP in comparison with all-electron Dirac–Fock results up to 32 eV excitation energy. The DF values are themselves in error by 1–3 eV on the average compared to experiment, but the present CI calculations based on this RECP lead to considerably higher accuracy because of the importance of correlation effects in such determinations. Energy differences (12 cases) between states with the same number of electrons are computed to an accuracy of 0.1–0.2 eV in all cases after the spin–orbit interaction is included. These results compare favorably with those obtained by Häussermann et al. [Mol. Phys. 78, 1211 (1993)] with a ... 5s2 5p6 5d10 6s2 RECP and a corresponding larger AO basis to describe the more tightly bound electrons. Good agreement is found for the spectroscopic constants of the HgH molecule in its lowest four electronic states: X 2Σ+1/2, A1 2Π1/2, A2 2Π3/2, and B 2Σ+1/2 (maximal errors of 1000 cm−1 for Te, 0.03 A(ring) for re and 150 cm−1 for ωe).An RKR curve reported for the A1 state is shown to be in error beyond r=4.0 a0 because of its failure to describe a key avoided crossing with the B state. Radiative lifetimes computed for the A 2Π multiplets are both found to agree with values deduced from experiment to within 40%. The calculations find no difference in the HgH and HgD radiative lifetimes for either the A1 or the A2 states, whereas a large distinction in the measured A1 lifetimes of the two isotopomers is observed, thereby supporting the previous experimental conclusion that strong predissociation occurs in the HgH A1 state. Numerous higher-lying electronic states are also studied, with Te values up to 60 000 cm−1, and on this basis it is argued that earlier assignments for the HgH C–X and D–X transitions are incorrect, as previously concluded by Nedelec et al. [Chem. Phys. 134, 137 (1989)]. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.471162
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  • 10
    Electronic Resource
    Electronic Resource
    Electronic states and transitions of tellurium fluoride (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 8386-8394 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Ab initio multireference configuration interaction calculations including spin–orbit coupling are carried out for valence electronic states of the TeF molecule and compared to the results for the isovalent IO system obtained earlier at a similar level of theoretical treatment [S. Roszak et al., J. Phys. Chem. A 104, 2999 (2000)]. The calculated spectroscopic constants are in good agreement with available experimental data. It is shown that the X 2Π(σ2π4π*3) ground state is much more strongly bound in TeF (calc. De=25 480 cm−1) due to the greater ionic character of bonding in this system as compared to IO. The lowest excited states of TeF are found to be A 4Σ1/2,3/2− and B 2Σ1/2− which result from the π→σ* electronic excitation. In contrast to IO, the 2Π(σ2π3π*4) excited state has a repulsive potential curve and is not expected to be a factor in the low-energy spectroscopy of TeF. Particular emphasis is placed on computation of the transition moments and radiative lifetimes of the TeF electronic states. Most transitions are found to be quite weak, with the strongest of them, B 2Σ1/2−→X1 2Π3/2, characterized by a τ value of 9.5 μs. The two C 2Δ spin components, Ω=5/2 and 3/2, not yet observed experimentally, are predicted to lie ∼1800 cm−1 above B 2Σ1/2− and have partial lifetimes for transitions to the X1 and X2 states which are only slightly longer than those calculated for the B→X1,2 transitions. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1362324
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